I have a 250 pound feeder it will hold 3 bags of game fish chow (50 Pounds a bag) This will last me around 2 to 3 weeks.

You might start out with a 400 pound feeder.
It will be close to what you should need in the long run.

Keep in mind if you are stocking the catfish from scratch, they will not eat as much when they are small but will gradualy eat more as they grow larger.

You should only feed them as much as they can eat in 15 min., so you will have to watch them eat their food from time to time and adjust the timer on your feeder to match their rate of food consumption.

Sounds like a good project to me. Good Luck to ya

Don